Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$29.90	10.807%	$33.1313	$33.13	$33.15	$33.10
Purchase #2	$240.94	7.511%	$259.037	$259.04	$259.05	$259.00
Purchase #3	$204.59	13.765%	$232.7518	$232.75	$232.75	$232.80
Purchase #4	$204.77	8.569%	$222.3167	$222.32	$222.30	$222.30
Purchase #5	$123.94	3.385%	$128.1354	$128.14	$128.15	$128.10
Purchase #6	$99.44	13.449%	$112.8137	$112.81	$112.80	$112.80
Purchase #7	$49.75	6.429%	$52.9484	$52.95	$52.95	$52.90
7 purchase totals =	$953.33		$1,041.1343	$1,041.14	$1,041.15	$1,041.00